Sonar devices are well known in the art and find widespread use in sport fishing, navigation, scuba diving, as well as any number of other recreational or commercial activities. Typically, a sonar system will include a sonar unit, which includes a display for providing information to the operator, and a transducer which is mounted under the waterline for generating an ultrasonic pulse and receiving echoes from objects in the water, or the bottom surface. The electronic circuitry for driving the transducer to transmit an acoustic pulse and for amplifying and filtering received echoes has traditionally been located in the sonar unit. Locating such circuitry in the sonar unit has, heretofore, provided a number of advantages, such as: there is more likely to be ample room for the circuitry in the sonar unit while the transducer tends to be comparatively small; the environment of the sonar unit is relatively benign, at least when compared to the environment of the transducer; and the cost of replacing a lost or damaged transducer is less when its associated circuitry is located remotely.
In such a system, driver circuitry in the sonar unit produces a pulse consisting of several cycles of an ultrasonic signal at a fairly high output power. This pulse is delivered to the transducer via a shielded twisted pair cable. After transmission of the sonar pulse, the transducer is typically used to “listen” for echoes. Received echoes produce very small signals, on the order of a few millivolts, which are sent via the transmission line to the receiver circuitry in the sonar unit. In the sonar unit, the received echoes are amplified, filtered, and analyzed.
It is widely accepted that some sonar frequencies are better suited for a particular purpose than other sonar frequencies. While most low priced sonar units operate at only a single frequency, and some moderate and high-end units add a second frequency, recreational sonar units operate at frequencies which represent a compromise designed to serve the sport fisherman reasonably well. Not only does a broader selection of frequencies allow tailoring of a sonar system for a particular environment, it allows multiple units to be used in a small area.
Today's transducers only provide depth, speed, and temperature data to the echosounder or fishfinder device which processes and displays the data to the operator.